Neural crest cells (NCCs) are responsible for proper embryonic development, especially that of the craniofacial and cardiac tissues. The sequence of events is complicated and poorly understood considering the common occurrence of birth defects resulting from abnormalities in these cells. Recently, the platelet derived growth factor receptor (PDGFR) has been implicated in NCC development based on cranial and cardiac phenotypes observed in null and NCC conditional animals. Preliminary data of genetic interactions between PDGFRa and PDGFR[unreadable] provides sufficient evidence that PDGFR[unreadable] plays a role in craniofacial and cardiac development as well. To investigate this hypothesis we have devised two specific aims: 1) To determine the developmental interactions between PDGFRa and PDGFR[unreadable] in craniofacial and cardiac development and 2) To identify the discrete NCC populations controlled by PDGFRa and PDGFR[unreadable]. This unique system allows us to study the direct role of the PDGFRs in NCCs and to identify how they direct NCC proliferation, migration, and differentiation in the cranium and the heart. [unreadable] [unreadable]